1. Field of the Invention
This invention relates to a method for finishing elastic O-ring gaskets to extremely close tolerances and to apparatus for performing that method. More particularly, the invention relates to a method of presenting an unfinished, endless length of elastic O-ring feed stock to the grinding surface of a centerless grinder and to apparatus for effecting such presentation and grinding the feed stock to a finished condition.
2. Description of the Prior Art
One conventional method of manufacturing elastic packing rings or O-ring gaskets of generally circular cross section, involves the extrusion of a moldable plastic rubber compound to form a preform rod of suitable cross section, and thereafter cutting the rod to length and inserting it into a mold in which a fused joint is developed between abutting rod ends during heat cure. It has been found that producing O-rings by this method frequently results in weak joints at which failures occur.
Another conventional method of making O-rings is to die-cut a circular preform ring from a calendared flat sheet of stock, and to then mold and cure the preform to final O-ring shape and dimension. O-rings produced by this latter method have no mold fused joint, but they are defective as to strength because the grain of the stock is not uniform throughout the ring, but on the contrary parallels the walls on two sides and is transverse thereto on the other two sides.
It has also long been known to fabricate O-ring gaskets to finished condition by a molding process intended to overcome the above defect. Thus, U.S. Pat. No. 2,646,595 discloses a method wherein a jointless, cylindrical preform is cut into rings which are then shaped, pressure molded and heat cured to final dimensions.
U.S. Pat. No. 2,954,263 teaches a method of simultaneously forming a plurality of elastic O-rings suitable for use as sealing members wherein a moldable plastic mixture is calendared and circumferentially lapped and compressed on an undulated mandrel to form a jointless, tubular preform with an undulated inner surface on the mandrel. The preform is pressure molded and heat cured in an undulated die to form an undulated outer surface on the preform to complement its inner surface thus to define a plurality of O-rings of final shape and dimension on the mandrel. The O-ring forms, bonded together at their sides, are pulled apart.
Techniques and apparatus for forming endless belts are disclosed in U.S. Pat. Nos. 1,917,548, 2,588,647, 3,891,405 and 4,782,575. From these it is known to build a belt preform on a mandrel, for example, and then to grind or cut the preform to the desired shape.